1. Field of the Invention
This invention relates to a quietly operating and easily manufactured power seat apparatus for automotive vehicles.
2. Description of the Prior Art
As shown in FIGS. 1 through 3, a power seat 1 for automotive vehicles includes an upper rail 3 to which a seat cushion 2 is fastened, and a lower rail 4 secured to the vehicle body and along which the upper rail 3 is moved back and forth. In order to so move the upper rail 3, a speed reducer 5 and a motor 6 are fixedly secured to the lower rail 4 and the speed reducer 5 is coupld to a screw shaft 7 attached to the upper rail 3. As shown in FIG. 3, the speed reducer 5 includes a worm wheel 8 having a threaded bore threadedly engaged with the screw shaft 7, a worm 9 engaging with the worm wheel 8, and a housing 13 accommodating the worm wheel 8 and worm 9. The speed reducer 5 also has an input shaft 10 connected to an output shaft 11 of motor 6 via a coupling 12.
The rotational torque produced by the motor 6 is transmitted to the input shaft 10 via the coupling 12 and has its direction changed by the worm 9 and worm wheel 8. The rotation of the worm wheel 8 inside the housing 13 causes the screw shaft 7 to move back and forth with respect to the lower rail 4 owing to the threaded engagement between the screw shaft 7 and the threaded bore of the worm wheel 8. This makes it possible to move the seat back and forth.
As shown in FIG. 3 and as set forth in the specification of U.S. Pat. No. 2,927,627, the coupling 12 in the prior-art arrangement of FIG. 3 is bonded to the input and output shafts 10, 11 by vulcanizing a resilient material such as rubber. If the bonding by vulcanization is not carried out after the input and output shafts 10, 11 are centered on each other with a high precision, the shafts 10, 11 may become off-centered. This can cause internal stresses that will quickly lead to deterioration of the apparatus. Furthermore, since the coupling 12 is bonded by vulcanization, the manufacturing costs are high.